OTTAWA — The Liberals dug up formidable mounds of dirt to throw at Stephen Harper during the election campaign — from leaked reports to clandestine recordings.

Yet none of it seemed to muddy the portrait of the prime minister — one that Canadians have grown increasingly comfortable with over five years of minority rule.

The Conservative leader is poised to win his third mandate from Canadians despite the fact the Tories’ 2011 campaign has been rocked by a steady barrage of incoming political artillery, much of it from Liberal researchers.

The digging by the Liberals was substantive. Among other things:

They snagged a tape recording of an anti-abortion Conservative candidate bragging about the defunding of an international agency that promotes family planning.

They released a note written by the man who advises the Conservatives on firearms policy that compared the Ontario Provincial Police to the Nazi SS and a Mussolini-era fascist paramilitary group.

They procured a 500-page dossier of potentially damaging remarks made by Harper over the years — a binder the Conservatives actually prepared as a defensive measure — that categorizes the PM’s utterances on everything from abortion to western alienation dating back decades.

Other political bomblets littered the campaign trail.

These included a leaked draft of an auditor general’s report that accused the Tories of misleading Parliament on G8 spending projects, headlines that alleged Harper’s chief spokesman peddled influence in Quebec, and an outcry over the barring of perceived political opponents from party rallies.

“They’ve thrown virtually everything they can at Stephen Harper and the Tories and none of it has stuck,” said Barry McLoughlin, one of Ottawa’s foremost media-messaging experts.

“Part of the problem is Stephen Harper has already been defined over the last five-year period. People feel they know who he is and, warts and all, they’ve figured him out. So that would be called fear of the known.”

Former Liberal strategist John Duffy shares the view.

He says much of the so-called dirt has simply reminded Canadians of what they already know about the Conservative government — “that it is secretive, that it contains social conservative elements, that it has a closed governing style.”

Harper is such a known quantity now that anyone who wants to can background themselves on the prime minister’s sentiments on a whole range of issues, said Duffy.

That’s makes finding the proverbial game-changer extremely difficult.

“I don’t know: what’s the killer quote? Good God, he called Canada a semi-socialist state — I don’t know. Unless it’s a howler line, something racist or sexist or homophobic, I don’t think there are any howlers in there that I’ve been able to find,” said Duffy.

Elly Alboim, a journalism professor and principal with the Earnscliffe Group, said the Tories have proven adept at stonewalling and deflecting any obstacle that throws them off-message. Of all the parties, they have become the most impervious to external shocks.

“The prime minister and the Conservative party, for good or for ill, have a character and a personality, and most people know what they are,” said Alboim, who has also served as an adviser to former Liberal prime minister Paul Martin.

Alboim and McLoughlin agreed that the Liberal attacks may have had one unintended consequence — inadvertently bolstering the NDP and propelling them up the polls past the Liberals to a tight second place with the Tories.

“My own personal theory — and there’s no evidence for it — is the NDP surge is very much a protest vote. Nobody has decided that Layton should be prime minister or they love NDP policies,” said Alboim.

McLoughlin said the Liberal attacks on Harper, may have “loosened up those voters and drove them all over to Jack Layton.”

The Liberal digging may have served one useful function, said Duffy. It may not have knocked the feet out from under the Harper campaign, but it may have kept it from soaring into majority-government territory.

“They must be frustrated that they haven’t been able to bring together more positive energy around their chosen theme of economic recovery, jobs and growth,” said Duffy.

“That’s the beachfront real estate of Canadian politics. They own it, but they haven’t been able to get above the ceiling.”